q1.1

Fe2+ config is 1s2 2s2 2p6 3s2 3p6 3d6

as

Fe is 1s2 2s2 2p6 3s2 3p6 3d6 4s2

2 electrons are lose from 4s2

q1.3

Aluminium, as the outermost electron is in a higher orbital (3p)m compared to that of Magnesuim (3s). hence requires less energy to remove.

q5.3 - Ph3 is trigonal pyrimidal due to 3 bond pairs and 1 lone pair
ch3cl is tetrahedral

for 7.2, I also said the hydoxide ion, as Magnesium hydroxide is a solid. - as OH solubility decreases going up the group.

Make sure you have state simbles for the equations, otherwise no marks !
Aqeuous reactants and solid products.

q8.6 = 3.78 gdm^3

q13 is B

Q14 is B
Q15 is D (Unsure)
Q16 is B (Increases titre value as some water may be remaining in the burette)
Q17 - unsure
Q18 is C ( rest are tetrahedral - C is Square Planar)
Q19 is D ( Eq constant only affected by temp, rest of answers are false)
Q20 is B as oxidation states are the same
Q21 is A (E- closes to nucleus)
q22 is C
q23 is A (Rest of the products are formed)

(edited 6 years ago)

Reply 94

SamDD

I'm also A2 and I've done the paper, but i can't seem to understand where people are getting some of the answers from.

For the one asking about the Mg excess and the q = mct question, surely the answer would be -91kjmol-1?

In the working above people have been dividing q by the number of moles of the zinc, and I am sure that you are supposed to do it with the moles of magnesium, as that is the thing being added and the zinc sulfate is the solution which is essentially acting like the water bath.

Also, for a later question I got 624 tonnes of rock required, as working out a mole ratio from the last question's equations it's roughly 1.5 moles of copper to 1 mole of CuFS2, hence you'd work out the moles of copper and divide it by 1.5 and then times it by the Mr of CuFS2 to get around 7.8 tonnes.

You'd then divide the 7.8 tonnes by 1.25% to get the total amount of rock required which comes to about 624 tonnes.

Furthermore, I can confirm that it is hydroxide ions used in the negative ion test, as Mg(OH)2 is sparingly soluble which means it pretty much just doesn't dissolve and you'd get a white precipitate forming, and to my knowledge MgCO3 and MgCl2 are both soluble at room temperature.

Also, I got -391 and +391 respectively for both of the enthalpy change calculations.

I'm not going to talk a bout that quadratic one, because I honestly have no idea, I dropped maths at AS for a reason (because I can't do it) so I don't think it's fair to stick bloody algebra on a chemistry paper!

(edited 6 years ago)

Reply 95

username1869653

Original post by hafsa473

This is the unofficial mark scheme for AS Chemistry 7404/01

First questions -
Configuration of
Fe2+ is 1s2 2s2 2p6 3s2 3p6 4s2 3d6
Cl- is 1s2 2s2 2p6 3s2 3p6

1 b) which has the lower first ionisation energy, aluminium or (magnesium?) ---- aluminium

There was a question on bonding which gave four different molecules. I think there were two tetrahedrals, there was BeCl2 which is linear (I think) and a trigonal planar, I believe. I think the only one with permanentent dipole dipole forces was Ch3Cl (but I could be confused with an MCQ on bonding)

A MCQ asked which of the products is note formed from a redox reaction between sodium iodide and sulfuric acid. I believe the answer was NaHSO4.

4050kg rocks - answer is around 963 tonnes

6 marker on improving methods

Equilibrium question on P, Q and R - 0.97

I got the expression for R as 2x
So kc= (2x)^2/(1-X)^2
Kc= 3.6 I think
So I square rooted it and then worked from there.

Enthalpy question - around 391 kj/mol

Q = mc∆t --- 50 × 4.18 × 31.7 or something
Overall enthalpy change is -155.9

What was in excess? Magnesium

concentration of sodium nitrite in g.dm^-3.
I got 3.71 g mol^-1

2 reasons on why so2 is removed (2 marks) (because it caused acid rain & it can be used as gypsum?)

4 marker on 2 reactions which produced white precipitates, and asked which two ions were present; i wrote ba2+, and cl-
-1 maker on definition of electronegitivity
-there was a question on working out RMM & which ion would reach detector quickest

Reply with anything you remember so I can add to this mark scheme!!

Fairly sure that everyone got the rock question incorrect. From what I can see, everyone answered the question in Isolation even though they were given equations to balance for the reaction to produce the Cu from the Cu compound earlier in another part of the same question. Unless I am overthinking it. But I don't think I am.

Reply 96

username1869653

Original post by SamDD

I think you are right about the rock question. Did the same thing and got the same answer. Everyone else seems to have missed out on the key step.

Reply 97

SamDD

Original post by ugaaa5

Nah, I think using the equations is correct.

It's a bit of a nasty question, as it relies on you getting the previous equations correct to gain 4 marks which is a bit mean I think.

I think a lot of people assumed it'd just be a 1:1 ratio, as they both contain copper but you'd need to work out the molar ratios for the reactions.

Reply 98

vali7654321

Original post by SamDD

I'm also A2 and I've done the paper, but i can't seem to understand where people are getting some of the answers from.

For the one asking about the Mg excess and the q = mct question, surely the answer would be -91kjmol-1?
In the working above people have been dividing q by the number of moles of the zinc, and I am sure that you are supposed to do it with the moles of magnesium, as that is the thing being added and the zinc sulfate is the solution which is essentially acting like the water bath.
Also, for a later question I got 624 tonnes of rock required, as working out a mole ratio from the last question's equations it's roughly 1.5 moles of copper to 1 mole of CuFS2, hence you'd work out the moles of copper and divide it by 1.5 and then times it by the Mr of CuFS2 to get around 7.8 tonnes.
You'd then divide the 7.8 tonnes by 1.25% to get the total amount of rock required which comes to about 624 tonnes.
Furthermore, I can confirm that it is hydroxide ions used in the negative ion test, as Mg(OH)2 is sparingly soluble which means it pretty much just doesn't dissolve and you'd get a white precipitate forming, and to my knowledge MgCO3 and MgCl2 are both soluble at room temperature.
Also, I got -391 and +391 respectively for both of the enthalpy change calculations.
I'm not going to talk a bout that quadratic one, because I honestly have no idea, I dropped maths at AS for a reason (because I can't do it) so I don't think it's fair to stick bloody algebra on a chemistry paper!